Building substantial "pure" 2 tier CouchApps - feasible?

[Andrew Stuart (SuperCoders)]

I'd like to build a rather substantial application, it would be nice  
to build it as a pure 2 tier CouchApp.

How practical is this really?  Does anyone have experience building  
anything big in this way?  Or are 2 tier CouchApps really only  
effective for small stuff?

I understand that it very much depends on what the app does, but I'm  
trying to get a general sense of it.

If pure 2 tier CouchDB apps is an impractical goal then we'll design  
the architecture from the beginning as a 3 tier app and whack in some  
sort of server.

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